Manufacture of alkyl lead compounds



Patented Apr. 1, 1952 MANUFACTURE OF ALKYL LEAD COMPOUNDS George Calingaert, Geneva, N. Y., and Hymin Shapiro, Detroit, Mich., assignors to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application April 30, 1951, Serial No. 223,815

6 Claims. 1

This invention relates to a new process for making alkyllead compounds.

The most important of the alkyllead compounds is tetraethyllead which is made commercially by reacting monosodium-lead alloy with ethyl chloride in accordance with the following equation process for increasing the yield of tetraethyllead obtained in the present process. Another object is to provide a process using free lead, thus avoiding the expensive alloying operation.

The above objects are accomplished by reacting an alkylating agent as hereinafter defined with lead and an alkylcadmium compound.

There are two types of alkylcadmium compounds 'which can be successfully employed in our invention. One is RCdX in which R is an alkyl radical and X is a halide and the other is RzCd in which R, is an alkyl radical. The reactions involving the two alkylcadmium compound types can be generalized by the following equations:

It should be noted that the theoretical yield of the alkyllead compound based on the lead is four times that of the present commercial process.

Any of the alkylating agents heretofore used or described for the manufacture of alkyllead compounds in the prior art can be used, among which are the alkyl halides, preferably the iodides, bromides and chlorides, the dialkyl sulfates and the trialkyl phosphates. In general, the alkylating agents are esters of inorganic acids having the proper alkyl groups for making the desired alkyllead compound, and having an inorganic acid group which forms a salt with the cadmium. Among those which can be used in our invention are the ethyl, propyl, and butyl chlorides, as well as the corresponding bromides and iodides, diethyl sulfate and.triethyl phosphate.

-Cata'lysts, while not essential to our invention;

do improve the yield. The catalysts useful in our invention can be generally characterized by their reaction with cadmium, i. e., they are those compounds containing an atom capable of chemically coordinating with cadmium, such as nitrogen or oxygen. Such chemical coordination is well known in this art. Among the catalysts falling in this category are the dialkyl ethers such as dimethyl, diethyl, and diisopropyl ethers and alkyl amines such as trimethylamine, triethylamine, tripropylamine and such compounds as triethylammonium iodide.

While tetraethyllead is the principal compound discussed herein because of its large commercial use, other alkyllead compounds such as tetramethyllead, tetrapropyllead, dimethyldiethyllead, and methyltriethyllead, can be made by the process of our invention. Likewise while we have referred to our process as a method of alkylating lead it is to be understood that arylating agents can be employed as well. These arylating agents are in general similar to the alkylating agents described hereinabove, and when this embodiment of our invention is employed the products are aryllead compounds, such as for example tetraphenyllead. Furthermore we can employ a mixture of alkylating and arylating agents, or alkyland aryl-cadmium compounds to produce thereby mixed arylalkyllead compounds.

Various alkylor aryl-cadmiums can be used depending on the lead alkyl desired such as the methyl, ethyl, propyl, butyl and phenyl cadmium. If the alkyl group attached to cadmium is different than the one attached to the alkylating agent a mixture of alkyllead compounds usually results.

For the best results a slight stoichiometric excess of the alkylcadmium should be used although lesser amounts give proportionate yields and will result in an increase in yield when used concurrently with the present process as described hereinafter.

The temperature employed is not critical, the preferable range being between about 50 and C. The pressure used is notcritical but should be suflicient at the temperature employed to maintain the alkylating agent in the liquid phase. The time of reaction is between about 30 minutes and 5 hours. The amount of alkylating agent employed is not critical but an excess over the stoichiometric amount required in the above general equation is preferred.

Our process can be used concurrently to improve the yield of the present commercialiproc- 'ess or it can be used independently in treating the unreacted lead from the present process or other forms of free lead. By concurrently is meant either adding the alkylcadmium along with the other reactants to the present process or first conducting the reaction of the present process and then adding the alkylcadmium together with additional alkylating agent if required. Such an overall reaction is expressed by the following illustrative equations corresponding to Equation 1 and 2 previously given herein:

wherein R is an alkyl group and X is a halide. Also, in place of sodium other metals, generally the alkali earth and alkali metals, well known for this purpose, can be alloyed with the lead and used in the above reaction. Among such metals are potassium, calcium and magnesium.

'Our invention can best be understood by referring to the following typical working examples in which all the parts and percentages are by weight.

' Example 1 Two-stage reaction using sodium-lead alloy and ethyl chloride: A charge of 100 parts of NaPb alloy is added to a reaction vessel, equipped with an agitator, a jacket for circulation of heating or cooling liquids, a reflux condenser, charging and discharging port, liquid feed lines, and means for releasing the pressure. Liquid ethyl chloride in the amount of 112 parts is added under pressure to the stirred solids in the vessel over a period of one-half hour. By controlling the flow of liquid in the autoclave jacket and in the reflux condenser the temperature of the reaction mass is permitted to rise from an initial temperature of 50 C. to a temperature of 70 C. during this feed period. The pressure in the autoclave during this feed rises to 75 pounds per square inch gauge where it is maintained. The temperature of the stirred reaction. mixture is maintained at 70 C. for an additional 15 minutes maintaining the '75 pounds pressure. For the second stage, an additional quantity or 84 parts of ethyl chloride with which has been premixed 38.8 parts of diethylcadmium and 24 parts of diethyl ether, is added uniformly under pressure to the autoclave over a period of 15 minutes, again maintaining the 75 pounds pressure. The temperature of the stirred reaction mass is maintained at 80 C., while maintaining '75 pounds pressure, for an additional 85 minutes. At the end of this period the pressure in the autoclave is reduced to atmospheric by venting for a 15 minute period at 70 C. Nitrogen is passed over the reaction mass while the autoclave is open to the atmosphere. The mass is then cooled to 45 C.

over an additional 30 minute period while flushmg with a stream of nitrogen. The reaction mass is then discharged slowly to a steam-still containing 250 parts of water. With lD-steam fed to the jacket of the steam-still, a forecut of ethyl chloride is taken, up to a vapor temperature of 70 C. At this point the steam jets are turned on, and with the jacket steam off the tetraethyllead is distilled for one and one-half hours after the first drop of tetraethyllead appears in the distillation receiver. The yield of product is 63.0 parts, or a yield of 45 per cent based on the lead present in the sodium-lea alloy.

Example II In the same equipment described in Example I, parts of lead recovered from an operation similar to that described as the first stage of Example I was treated with 250 parts of ethyl chloride premixed with 57.5 parts of diethylcadmium and 35 parts of diethyl ether. The reaction was conducted in the same manner as in the second stage of Example I. The product obtained in this reaction was 49.5 parts of alkyllead, corresponding to a yield of 31.8 per cent based upon the lead charged to the reactor.

Example III In a series of operations similar to Example I and in the equipment of that example, 100 parts or" sodium-lead alloy was treated with 112 parts of ethyl chloride according to the procedure for the first stage in the above example. At the end of this stage an additional quantity of 84 parts of ethyl chloride with which had been premixed parts of ethylcadmium iodide and 24 parts of diethyl ether was added to the autoclave over a period of 15 minutes at a pressure of 75 pounds per square inch guage. After carrying out the steps of the second stage and recovering the product therefrom the yield of tetraethyllead was 48.? parts or 35.8 per cent based on the lead present in the sodium-lead alloy.

In operations similar to Example I when methyl chloride, ethyl bromide and ethyl iodide were used as the alkylating agents, yields based on the lead present of 56 per cent, 47 per cent, and 77 per cent respectively were obtained. Similar good results are obtainable when in place of ethylcadmium iodide, methylcadmium iodide, propylcadmium iodide, ethylcadmium bromide and ethyl cadmium chloride are used.

Further in operations similar to Example III when ethyl bromide and ethyl iodide were employed as the alkylating agents, yields of 23 per cent, and 47 per cent, respectively, were obtained, based on the lead employed.

In another operation similar to Example I in which no catalyst was used, employing diethylcadmium and ethyl iodide, a yield of 64 per cent based on the lead was obtained.

Thus the above examples illustrate that almost a fourfold increase in yield over that obtained in the present commercial process can be made by our process. It must be appreciated however that in the above examples the amount of alkylcadmium compound is less than that required to completely alkylate the lead as in equations 1 to 4 and such examples do not represent the maximum yield obtainable by our process.

Other embodiments of this invention can be made without departing from the spirit and scope of our invention which is not limited to the specific embodiments given herein.

We claim:

1. A process for making alkyllead compounds comprising reacting lead with an alkylating agent which includes the hydrocarbon radical in question and having a negative radical which reacts with cadmium, and with an alkylcadmium compound having the formula RCdX wherein R. is alkyl and X is a member of the group consisting of alkyl and halide.

2. The process of claim 1 in which the alkylcadmium compound corresponds to the formula RCdX in which R is an alkyl radical and X is a halide.

3. The process of claim l-in which the alkyl- 5 cadmium compound corresponds to the formula RzCd in which R is an alkyl radical.

4. The process according to claiml for making tetraethyllead which comprises reacting lead with an excess of an ethylating agent in the presence of an ethylcadmium compound having the formula RCdX wherein R is ethyl and X is a. member of the group consisting of ethyl and halide 5. The process according to claim 4 in which the ethylating agent is ethyl chloride.

6. A dual process for making tetraethyllead which comprises reacting a sodium-lead alloy with ethyl'chloride and reacting the free lead so produced with ethyl chloride in the presence- 2,575,323

GEORGE CALINGAERT. HYMIN SHAPIRO. REFERENCE/S CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,558,207 Calingaert et al. June 26, 1951 2,562,856 Calingaert et al. July 31, 1951 Shapiro et a1 Nov. 20, 1951 

1. A PROCESS FOR MAKING ALKYLEAD COMPOUNDS COMPRISING REACTING LEAD WITH AN ALKYLATING AGENT WHICH INCLUDES THE HYDROCARBON RADICAL IN QUESTION AND HAVING A NEGATIVE RADICAL WHICH REACTS WITH CADMIUM, AND WIT AN ALKYLCADMIUM COMPOUND HAVING THE FORMULA RCDX WHEREIN R IS ALKYL AND X IS A MEMBER OF THE GROUP CONSISTING OF ALKYL AND HALIDE. 